This invention relates to the use of optical fibers, and, more particularly, to an assembly of an optical fiber and a support material that provides improved performance in situations wherein the optical fiber is dispensed from a canister.
Optical fibers consist of strands of optically pure glass fiber processed so that light beams transmitted therethrough are subject to total internal reflection. A significant fraction of the incident intensity of light directed into the fiber is received at the other end of the fiber, even though the fiber may be hundreds or thousands of meters long. Optical fibers have shown great promise in communications applications, because a high density of information may be carried along the fiber and because the quality of the signal is less subject to external interferences of various types, as compared to electrical signals carried on metallic wires. Moreover, the glass fibers are light in weight and made from a highly plentiful substance, silicon dioxide.
Glass fibers are typically fabricated by preparing a preform of glasses of at least two different optical indices of refraction, one inside the other, or a single glass composition with a coating that ensures total internal reflection, and processing the preform to a fiber by drawing, extruding, or other method. The optical fiber is then coated with a polymer layer termed a buffer coating to protect the glass from scratching or other damage. As an example of the dimensions, in a typical configuration the diameter of the glass optical fiber is about 0.005 inches, and the diameter of the optical fiber plus the polymer buffer coating is about 0.006-0.010 inches.
For such a very fine optical fiber, the handling of the optical fiber to avoid damage or stresses that might reduce its light transmission properties becomes an important consideration. The optical fiber is typically wound onto a cylindrical or tapered cylindrical substrate, called a "bobbin", having many turns adjacent to each other in a side by side fashion to form a layer. After one layer is complete, another layer of optical fiber is laid on top of the first layer, and so on. The array of wound optical fibers is termed the "fiber pack", and the final assembly of the bobbin and the wound layers of optical fiber is termed a "canister". At a later time when the optical fiber is used, the optical fiber is ordinarily payed out from the canister in an unwinding operation, with the speed of unwinding depending upon the particular application.
It has been found by experience that, where the optical fiber is payed out from the canister in a rapid fashion, the turns of optical fiber must be held in place on the canister with an adhesive that holds the fiber pack together. The adhesive holds each turn of optical fiber in place as adjacent turns and layers are initially wound onto the canister, and also as adjacent turns and layers are payed out. Without the use of an adhesive, payout of the optical fiber may not be uniform and regular, leading to multiple dispenses (payout of two or more layers simultaneously), snags or other irregularities that damage or cause the optical fiber to break as it is payed out from the canister.
The successful dispensing or payout of the optical fiber from the canister is highly dependent upon the adhesive application and formulation. Conventional adhesives are applied to the turns of a layer after the layer is wound onto the bobbin. The deposition of the adhesive therefore requires an interruption to the winding process when each layer of optical fiber is deposited. Equally of concern, the deposition of the adhesive in precisely the correct amount is partly a handwork operation performed by a craftsman. Individual variations in application of the adhesive can lead to variations in the performance of the canister. If too little adhesive is applied in a region, multiple turns may be dispensed at once with a resulting snarl and breakage of the optical fiber. If too much adhesive is applied in a region, the stress required for payout may be too large, causing distortion or breakage of the optical fiber. If too much adhesive is applied in a region, the stress required for payout may be too large, causing distortion or breakage of the optical fiber.
The formulation of the adhesive is also a concern. Existing adhesives are neoprene based, and may become brittle at low temperatures. The brittle adhesive can cause an irregular payout because the adhesive must be fractured at the point where the dispensed portion of the fiber separates from the remaining turns.
Thus, the use of an adhesive to hold the optical fiber in place on the bobbin is a critical aspect of the optical fiber system using such a canister payout approach. There is a continuing need for improvement to this aspect of the dispensing system. The present invention fulfills this need, and further provides related advantages.